Live Coverage of the Blizzard for tonight through tomorrow

I’m going to start live coverage of this storm now with sporattic updates through the day.  Intense live coverage and question/answer periods will start after 7:30 PM.   Tonight at 9:30 PM, I will be discussing the storm on Tri-State weather Radio!

Blizzard conditions expected from Philadelphia through New York City

8:22 AM

A significant winter storm is beginning to develop over the Gulf Coast that will bring the entire forecast area heavy snowfall and very strong winds.  The most significant impacts will be focused towards the coastal plain once again, where many locations have experienced one of the snowiest winters of all time.  This storm will likely push this year’s snowfall totals to number one on the list, especially around central and southern New Jersey and Philadelphia.

This morning, the water vapor satellite image shows the developing upper level disturbances that will produce this dangerous winter storm.  The Polar disturbance is diving towards the Ohio Valley with a weak surface representation over the northern Tennessee Valley.  Meanwhile, the Sub Tropical disturbance is starting to tilt negative and beginning to phase with the Polar disturbance.  The phasing of these two disturbances will create an intense upper level low over the Ohio Valley and then Virginia that will spawn a rapidly deepening coastal low tonight through tomorrow off the Mid Atlantic coast.  The intensity of this low pressure will fall to below 980 MB possibly reaching 975 MB before exiting the New Jersey coastal waters.  This intense low pressure system will have plenty of moisture to work with from the Sub Tropical jet stream and a well established and sustained Polar air mass over much of the Mid Atlantic.

At 500 MB, an intense upper level low will move towards northern Virginia with intense PVA or positive vorticity advection moving towards the New Jersey coast.  Ahead of this upper low, there will be strong divergence from 500 MB up through 250 MB supporting an environment for rapidly rising air or lifting.  Due to the upper low intensifying, the surface low will feel the “pull” of the upper low and slow down the low pressure system to a crawl off the Delaware and southern New Jersey coastal waters between 7 AM and 5 PM tomorrow before slowly exiting into the Atlantic in the evening hours.  The influence of the upper low will lead to a prolonged period of moderate to heavy snow over the region as a result and support high snowfall totals.

The key to the forecast and the reason why I was hesitant to update much yesterday was the development of the 700 MB low.  There is now strong agreement in the model guidance that the 700 MB low will track from the Ohio Valley through south-central Virginia and then exit south and east of New Jersey.  The track of the 700 MB low is extremely important for this storm.  This current forecasted track, which again has rather strong agreement in the guidance, keeps the rapidly developing dry slot to the south and east of the northern Mid Atlantic with the possible exception of extreme eastern Long Island.  The track of the 700 MB low also puts much of the Philadelphia and southern New York City metropolitan area in an area of intense mid level forcing or lifting, which will likely support the development of various mesoscale features and keep the most intense precipitation over the region.  Studies have shown that the heaviest snowfall usually occurs 100 to 150 miles northwest of the 700 MB low, which is exactly where much of the forecast area is located.

At 850 MB, a strong low level jet stream is going to develop off the New Jersey coast as the 850 MB passes south and east of the region.  The strong low level jet stream will not only add significant Atlantic moisture to the developing coastal low pressure system, but also aid in supporting strong wind gusts over the region and intense mesoscale lifting.  The thermal gradient will also become very intense.  Some warmer air will work into southern New Jersey and eastern Long Island ahead of the 850 MB low, but otherwise the rest of the region will remain below freezing.  By late Wednesday morning, 850 MB temperatures will crash well below freezing, creating an environment that will be highly unstable throughout the coastal plain.  The combination of frontogenesis and this intensifying instability from the surface boundary layers to the mid level will create an environment highly supportive of convective snowfall, mesoscale banding, and there are some suggestions of an intense deformation zone developing on Wednesday evening as the storm exits.  The combination of these factors will lead to the potential for some locations to have enhanced snowfall totals compared to surrounding locations.

The worst impacts from this storm will be focused along the coast once again, however even interior locations will feel the bite from this storm as moderate snowfall amounts are expected even up through the Hudson Valley.  The worst conditions by far will be focused from southeastern Pennsylvania through much of New Jersey, the entire New York City metropolitan area and southern Connecticut.  Due to the warm air mixing in along the immediate coast, accumulations will be lower along southeastern and eastern Long Island and southeastern New Jersey, however even these locations will have a significant impact from this storm.  The strong wind gusts, potentially reach hurricane strength over the coastal waters, will create an environment of blizzard conditions with near zero visibility at times.  This can not be understated!  Even if a location accumulates 6 inches of snow, a strong wind of around 25 mph sustain will still keep visibilities on the low side.  The worst conditions for this storm can be expected from 3 AM to 8 PM over the Philadelphia metro, 5 AM to 10 PM for the New York City metro, and 7 AM to 1 AM over eastern Long Island and eastern Connecticut.

Snowfall totals will be the highest over the Philadelphia metro through the New York City metro.  The latest mesoscale guidance along with some analysis of the coastal front this morning suggests to me that the area from Monmouth County through Salem Counties have the best potential for convective snowfall including thunder snow due to the very unstable nature of the atmosphere and the combination of a very favorable alignment with the 850 MB low level jet stream.  However all locations along the coast will have the potential to get into a mesoscale snow band that can enhance snowfall totals.  Now, the issue with mesoscale features as always is that while one area can get hammered, another location to the east or west of that band can end up with significantly less snowfall than expected.  That situation will have to be NOW-Casted, but the potential is certainly there for someone to exceed two feet especially if the deformation zone sets up over the region.

This storm is going to have a significant impact on the entire northern Mid Atlantic for both major rush hours.  Due to this storm developing in the middle of the week, the impacts will be far more reaching than either major storms this year that occurred on the weekends.  Travel will be impacted from this storm and individuals should be prepared for dangerous driving conditions tomorrow morning and tomorrow evening.  In short, if you don’t have to go out, don’t!

After this storm exits, high pressure will take hold through the rest of the week with dry conditions and cold temperatures.  Another potential snow threat is emerging for Sunday into Monday, however currently the majority of the precipitation will remain well to the south.  For now, I’m advertising scattered snow showers.

TODAY’S HEADLINES

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WINTER FORECAST PUBLICLY RELEASED!

ANOTHER MAJOR WINTER STORM ON THE WAY!

ONE TO TWO FEET OF SNOW POSSIBLE FOR PHILADELPHIA AND NEW YORK CITY

HOWEVER QUESTIONS STILL REMAIN ON DETAILS

INTENSE CONVECTIVE SNOW BANDING EXPECTED

WILL LEAD TO SOME EXTREME SNOW GRADIENTS AGAIN!

MAJOR STRATOSPHERIC WARMING DRIVING NEW PATTERN

NEGATIVE EPO WILL LEAD THE WAY!

MJO REMAINS STRONG IN STAGE 7

HISTORY TEACHES THAT WINTER IS NOT OVER AND MORE IS TO COME

NORMAL CLIMATE DATA FOR JANUARY POSTED!

FOCUS ON 5 DAYS AT A TIME, AND YOU WON’T GO NUTS

LOCAL FORECAST DISCUSSION

New Snow Map Issued

6:58 AM

Here is the latest and final snow map before the winter storm.  A complete break down and analysis of this storm is on the way!

00Z Models Preliminary Thoughts

11:05 PM

The 00Z guidance confirmed my suspicion that the 12Z guidance was not handling the development of the 700 MB upper low correctly.

At this time,this storm is clearly going to have a major  impact on the entire northern Mid Atlantic.  While I likely will have to adjust some features on the snowfall map to the left, the overall idea that is presented here to the left.  I do think that the best areas for potentially one to two feet of snow will range from Philadelphia through central and northeastern New Jersey, through New York City, and into southern Connecticut.

Portions of northeastern Pennsylvania will likely remain closer to 10 to 12 inches rather than two feet based on the development of the 700 MB low on the guidance.

I will have more information tomorrow morning along with an updated snowfall map to illustrate the areas of best mesoscale dynamics and other factors.

Evening Thoughts: Heavy snow depends on mesoscale banding

9:30 PM

This evening I am in a waiting pattern before issuing any new snow maps at this time.  Through the day, the 12Z and 18Z model guidance has illustrated a potential limiting factor in the development of this dangerous winter storm.  The 12Z and 18Z GFS/NAM solutions basically follow the idea of the 700 MB low developing in such a way where heavy precipitation falls over the Baltimore metropolitan area and southern New England, yet lower QPF amounts for New York City.  The other feature is the development of mesoscale banding that reaches an apex over south-central New Jersey and then redevelops with increased mid level frontogenesis for Connecticut and the rest of the Southern New England.

What these two models are showing is the impact of strong lifting to the south and then north of the New York City metropolitan area, which leads to significantly less snowfall.  However, I stress that the way the mesoscale banding, especially the deformation zone, develops is very much uncertain and a rather fluid forecasting situation.  The location of this intense band, which on guidance produces up to two inches of liquid precipitation and up to two feet of snow, can just as easy develop over much of the New Jersey coast and the New York City metropolitan area.

So for now, I am going to take a wait and see approach with the 00Z guidance and then update appropiately for tomorrow morning, in which I’ll have an updated snowfall map and a break down of what to expect from this storm.

Regardless of the development of the 700 MB low, heavy snow is expected throughout much of the northern Mid Atlantic.  Strong wind gusts along the coast, will significantly reduce visibility and produce near blizzard conditions.

More on this dangerous storm for tomorrow morning!

12Z NAM Thoughts

9:55 AM

The 12Z NAM is out and to the left is the QPF output for the storm based on this run.  Now I know many of you in northeastern Pennsylvania, northern New Jersey, and even New York City are screaming right now in frustration.  Is the NAM forecasting a miss for these areas?  Well,not exactly.

What the NAM is showing here are two concerns that I addressed with this storm in this morning’s post.  The first being the development of the 700 MB upper low.  On this run, the 700 MB upper low is slightly and I mean SLIGHTLY further west than in other model guidance.  As a result, the dry slot for this storm drives right up the New Jersey coast and cuts right through Long Island, then slides due east as the 700 MB lifting features slide east towards the new coastal low.  This is a valid and significantly possible outcome, but not something that is written in stone.

The other concern is the development of convective banding of snowfall.  Let me be blunt, someone is going to miss out on this storm compared to their surrounding neighbors.  That location can easily be northeastern Pennsylvania, Philadelphia, or any other location throughout the forecast area.  What the NAM shows is that impact of such intense banding on the snowfall forecast.  Again, this feature will have to be nailed down in the hours up to and even through the development of this storm.  However, the NAM illustrates perfectly the type of resulting snowfall gradient that can develop with this storm.

So for now, I’m not changing the going forecast as a slight shift of the 700 MB features from this run puts the entire region in a QPF zone of over 2 inches.  The best position I would take is prepare for a significant impact and go from there.

Convective snowfall to play a key role on Wednesday

9:37 AM

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The forecasted soundings for Wednesday morning are rather interesting and will likely have a key impact on snowfall totals throughout the region.

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Another significant snowfall on the way

8:14 AM

Here we go again!  Another major winter storm has a target for the northern Mid Atlantic with the potential for another one to two feet of snow for many locations in the New York City and Philadelphia metropolitan area along with very strong winds and near zero visibility for Wednesday morning.

The water vapor satellite image this morning displays all the players for this major winter storm.  The first feature to take note of is the strong upper low, enhanced by the last major low pressure system, over the Canadian Maritimes.  That is the 50N/50W upper low that is key for any significant winter storm.  This upper low is in a near text book position to support a major to potentially historic winter storm for the region.  The position of this feature on all guidance strongly supports a stormy track from North Carolina to the bench mark.  Meanwhile the phase is starting to take shape over the central Plains between the Sub Tropical disturbance and Polar disturbance.  Note the streak of moisture racing out of the Southern Plains and into the Tennessee Valley.  This is the contribution from the Sub Tropical jet stream, which will become even more enhanced as the Polar disturbance, which is already rather intense, interacts with this jet stream of moisture.  Now, before going into the details of this storm, I should warn that I still think there are some issues with this storm that will need to be watched.

First, the position of the upper low on Tuesday evening is going to be very important.  The overall idea on the model guidance is that the trough axis of this intense upper low goes negative, which drives very strong PVA towards the Mid Atlantic coast.  Or in other words, very strong lifting is driven towards the coast leading to rapid low pressure development.  The speed and intensity of this transfer of energy from the old primary over the Ohio Valley to the new coastal low off the North Carolina coast will be extremely important.  If the transition is slower than forecasted, then several issues will unfold with the development of a heavy snowfall.  For one, if the 850 MB low is slow to develop along the coast, then much warmer air may work into the coastal plain causing a larger area of mixing than currently expected.  Or if the 700 MB low is slower or further west, then a dry slot may significantly cut snowfall totals in half.  These issues should be ironed out in the next two model runs this morning and tonight.  The trends seen on the 06Z guidance may be illustrating these issues or simply be a case of model error.  However, these issues will have to be ironed out.

The way I see this storm working out is that the coastal low pressure system will bomb out to the east of the New Jersey coast, reaching a pressure of around 978 to 972 MB by Wednesday afternoon.  This low pressure system will be capable of very strong wind gusts and coastal flooding.  The storm will also feature an area of intense deformation, which will lead to bands of heavy snowfall developing.  Temperatures will be falling through the day on Wednesday, causing snow ratios to rise from initially 10:1 up to 20:1 by storms end.

As of this morning, here are the storm impacts I envision for this winter storm.  High winds and coastal flooding will be an issue throughout the coast line regardless of precipitation type.  The high winds will range from 15 to 30 mph sustained with gusts over 40 mph expected.  The 950 to 850 MB low level jet stream is expected to drive right into the central New Jersey coast on Wednesday morning right through the evening hours, supporting the potential for wind gusts up to 70 mph at times, especially in areas of strong mesoscale banding.  As for precipitation types, some warmer air is expected to work into the lower and mid levels of the atmosphere over southeastern Long Island and southern New Jersey, leading to a mix of snow, sleet, and rain at times.  This wintery mix will hold down snowfall accumulations, however all precipitation will change over to snow by Wednesday afternoon.  Otherwise, intense heavy snowfall is expected throughout the New York City and Philadelphia metropolitan area with the potential of 1 to 2 feet of snow, near zero visibility at times, and very unfavorable driving conditions for the morning and evening rush hours over the region.  The difference in snowfall totals in this area will be determined by location of mesoscale banding features and the development of convective snowfall.  Where these features set up will determine what location gets the most snowfall.  Other considerations will be the speed in which temperatures at the surface and 850 MB falls to impact snow ratios in locations.

This storm is expected to exit late Wednesday night into early Thursday morning with a few lingering snow showers thereafter.  High pressure will take hold on Thursday afternoon through Saturday with clear skies and cold temperatures.  Temperatures through the period will average slightly below normal with many locations remaining in the upper 20’s to mid 30’s for afternoon highs.

Another area of low pressure may potentially impact the region on Sunday.  This low pressure system is currently expected to remain well to the south at this time, but may more far enough north to introduce some snow showers into the region.  Otherwise, the northern Mid Atlantic will get a few days rest after two major snow storms in a 5 day span.

Storm Watch Video For Sunday February 7, 2010

2:26 PM

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Another major storm is on the way, but there are some questions that should be considered before throwing out accumulation totals.  Find out what those issues are in this video!  Also, a discussion of the trends in the stratosphere and how long this stormy and cold pattern will last!

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